(got access to my books now

)
As detailed on p. 248 of Shadowrun, Fifth Edition, Patrol IC is typically always running in a host, constantly scanning for suspicious activity.
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Use the following chart to determine how frequently Patrol IC makes a targeted Matrix Perception Test against the hacker:
My reading is that this gives the Patrol IC no special power. It is a simple rule of thumb clarification for GMs how often the Patrol ICs in different hosts will do the Matrix Perception test for illegal behavior on the hacker's icon.
So if the Patrol IC would not rise the alert by the core it should not rise the alert by the DT.
Yes.
Re-reading the chapter and the example I tend to agree with this.
So, what does "scanning for suspicious activity" mean?
SR5 p. 235 Matrix Perception
When you take a Matrix Perception action, each hit can reveal one piece of information you ask of your gamemaster. Here’s a list of some of the things Matrix Perception can tell you. It’s not an exhaustive list, but it should give you a pretty good idea about how to use Matrix Perception:
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• The last Matrix action an icon performed, and when.
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"Suspicious activity" might be "Last Matrix Action";
That if the "Last Matrix Action" is a Sleaze or Attack Action then Patrol IC will not like what it sees and will sound an alarm...?
It is clear that running silent make it harder for the host to Spot you. However, once you show up on the hosts spotting list it seem as if it only need one hit on a simple matrix perception test to check your last matrix action...
Are intruders maybe supposed to use the Hide matrix action at regular intervals (assuming that the intruder can't really tell if the host actually spotted him or not) to continue to stay off the hosts spotting list in order to benefit from running silent...?
If you are just trying to search for a the correct SR5 File Icon (using the data processing matrix action "Matrix Search") then maybe you might as well do it while not running silent?
Thoughts?
What about not running silent and follow up all your illegal sleaze and attack actions with a legal data processing action (like matrix perception). Once the host get around to scan you odds are that it will show your last matrix action as Matrix Perception (or Change Icon, Edit File or Matrix Search etc). Not really suspicious activity...?
Actually... just being Spotted as Running Silent in a host that are not supposed to have any silent running icons might in itself be considered suspicious activity...?
I need to think about this.
Will you find the file through the search even if it is protected and within another protected file icon?
According to the table on p. 24; Information can be:
1) General Knowledge or Public
2) Limited Interest or Not Publicized
3) Hidden or Actively Hunted and Erased
4) Protected or Secret
Once you are in the host where the information is stored (but actually
finding the correct host will be tricky if the information is Protected or Secret) then you can find it with Matrix Search with a base time of 20 combat turns that you can reduce with extra hits... regardless of the kind of information you are searching for.
SR5 p. 241-242 Matrix Search
You can then make a Matrix Search within the host, using a base time of 1 minute (regardless of the kind of information you’re looking for). But the information also need to be at least occasionally accessed by a legitimate user (or else you need to go deep into the foundation and bring it out of archive).
SR5 p. 242 Matrix Search
This only works if the information is at least occasionally accessed by the legitimate users of the host. If the information is archived, you’ll need to dig deeper into the host for that information, a dangerous process that is detailed in the forthcoming Matrix sourcebook.To my knowledge you cannot "Enter File Icon" (like a "Node" or a "mini host") to get access to other SR5 File Icons
within the first....?